Mucormycosis is a life-threatening infection that occurs in patients immunocompromised by diabetic ketoacidosis, neutropenia, steroid use, and/or increased serum iron. Because of the rising prevalence of risk factors, the incidence of mucormycosis has dramatically increased (1300% over 15 years according to one source). Despite disfiguring surgery and aggressive antifungal therapy, the mortality of mucormycosis remains >50%, and approaches 100% in patients with disseminated disease. Clearly new strategies to prevent and treat mucormycosis are urgently needed. Clinical hallmarks of infection by Rhizopus oryzae, the most common cause of mucormycosis, include the unique susceptibility of patients with increased available serum iron, the propensity of the organism to invade blood vessels, and defective phagocytic function, which we hypothesize to be, at least in part, a result of iron toxicity. These clinical hallmarks underscore the critical role of iron metabolism, as well as interactions with endothelial cells lining blood vessels, in the organism's virulence strategy. We have found that R. oryzae damages endothelial cells in vitro and this process is dependent on iron. Additionally, we have cloned the R. oryzae high affinity iron permease (rFTR1) which scavenges iron from iron-depleted environments such as is found in the host. Finally we have developed clinically relevant models of infection in diabetic ketoacidotic mice. We hypothesize that iron uptake, and specifically rFTR1, is essential for R. oryzae to cause infection. To test this hypothesis, we propose to: 1) characterize the mechanism(s) by which iron regulates R. oryzae- induced endothelial cell injury;2) construct an isogenic rftrl null mutant and its corresponding rFTR1 complemented strain jn R. oryzae by site directed mutagenesis;3) compare the pathogenicity of the generated rftrl to that of the wild-type and rFTR1 complemented strains in our in vitro and in vivo models of infection;and 4) elucidate the role of iron in regulating the innate host response to R. oryzae. Accomplishing these specific aims will define the role of the central elements affecting the establishment and progression of mucormycosis as it relates to iron uptake. Ultimately, a superior understanding of the pathogenesis of mucormycosis will enable development of novel therapies for this disease. Completion of the proposed studies will enable investigation of treatments that block R. oryzae uptake of iron.